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#include "geometryengine.h"

#include <QVector2D>
#include <QVector3D>

struct VertexData
{
	QVector3D position;
	QVector2D texCoord;
};

//! [0]
GeometryEngine::GeometryEngine()
	: indexBuf(QOpenGLBuffer::IndexBuffer)
{
	initializeOpenGLFunctions();

	// Generate 2 VBOs
	arrayBuf.create();
	indexBuf.create();

	// Initializes cube geometry and transfers it to VBOs
	initCubeGeometry();
}

GeometryEngine::~GeometryEngine()
{
	arrayBuf.destroy();
	indexBuf.destroy();
}
//! [0]

void GeometryEngine::initCubeGeometry()
{
	VertexData vertices[] = {
		{ QVector3D(-1.0f, -1.0f,  1.0f), QVector2D(0.0f, 0.5f) },  // v0
		{ QVector3D(1.0f, -1.0f,  1.0f), QVector2D(0.33f, 0.5f) }, // v1
		{ QVector3D(-1.0f,  1.0f,  1.0f), QVector2D(0.0f, 1.0f) },  // v2
		{ QVector3D(1.0f, -1.0f,  1.0f), QVector2D(0.33f, 0.5f) }, // v1
		{ QVector3D(-1.0f,  1.0f,  1.0f), QVector2D(0.0f, 1.0f) },  // v2
		{ QVector3D(1.0f,  1.0f,  1.0f), QVector2D(0.33f, 1.0f) }, // v3
	};

	GLushort indices[] = {
		0, 1, 2,
		3, 4, 5
	};

	//! [1]
	// Transfer vertex data to VBO 0
	arrayBuf.bind();
	arrayBuf.allocate(vertices, 6 * sizeof(VertexData));

	// Transfer index data to VBO 1
	indexBuf.bind();
	indexBuf.allocate(indices, 6 * sizeof(GLushort));
	//! [1]
}

//! [2]
void GeometryEngine::drawCubeGeometry(QOpenGLShaderProgram *program)
{
	// Tell OpenGL which VBOs to use
	arrayBuf.bind();
	indexBuf.bind();

	// Offset for position
	quintptr offset = 0;

	// Tell OpenGL programmable pipeline how to locate vertex position data
	int vertexLocation = program->attributeLocation("a_position");
	program->enableAttributeArray(vertexLocation);
	program->setAttributeBuffer(vertexLocation, GL_FLOAT, offset, 3, sizeof(VertexData));

	// Offset for texture coordinate
	offset += sizeof(QVector3D);

	// Tell OpenGL programmable pipeline how to locate vertex texture coordinate data
	int texcoordLocation = program->attributeLocation("a_texcoord");
	program->enableAttributeArray(texcoordLocation);
	program->setAttributeBuffer(texcoordLocation, GL_FLOAT, offset, 2, sizeof(VertexData));

	// Draw cube geometry using indices from VBO 1
	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, 0);
}
//! [2]
